Production of pulp



v Patented May 23, 1933 No Drawing. Original application UNITED STATESPATENT OFFICE Lnnr BRADLEY, or momcnam, NEW JERSEY, AND nnwann r.MCKEEFE, 01 runs BURG,

PRODUCTION OF PULP This invention relates to a regenerative method forthe production of wood pulp with a cooking liquor containing sodiummonosulfite, or a mixture of sodium monosulfite' and caustic soda, andwith treatment of the residual liquors from such process for further usein the process. A

In certain companion applications Serial Nos. 481,147 and 711,857 wehave described a new and useful method of producing wood pulpfrom woodby subjecting the wood'to a cooking operation, under pressureand at anelevated temperature, with a cooking liquor consisting essentially ofsodium monosulfite, orsodium monosulfite together with a limited amountof caustic soda. Such processes result in the production of increasedyields of a superior and improved pulp, containing fibers of greatstrength, which have not been objectionably injured by the cookingoperation.

The present invention relates to improvements in such processes, and tothe treatment of the residual liquors from such processes, whereb theprocesses become regenerative or cyclic in character.

- The residual liquors produced by such pulp processes are ofdistinctive and characteristic compositiom They contain a decreasedcontent of organic matter, as compared with the black liquor from thesoda or sulfate process, due to the fact that incrusting and non-fibrousconstituents are dissolved or removed from considerable amount of thefibers themselves,

.whereas, in the soda and sulfate processes, a

considerable amount of the fibers is dissolved and goes into theresidual liquor.

The composition of the residual liquors which are treated according tothe resent invention will vary somewhat with different woods, and withthe particular composition of the cooking liquor. With deciduous woods,such as poplar, bass wood, maple, birch, beech, oak, etc., and withcertain coniferous woods, such as spruce, pines, etc., the cookingoperation may be carried out with a cooking liquor containingessentially normal sodium sulfite. With other woods, particularly highlyresinous woods, such as cer- Serial No. 203,267.

tain ines, the cooking liquor may contain- NEW YORK, ASSIGNORS TOIBRADLEY-MQKEEFE CORPORATION, 01' NEW filed February 7, 1922, Serial no.534,768. Divided and this application filed Ju1y'2, 1927. a

or caustic soda or both'with saponifiable constituents of the woodtreated, particularly in the case of resinous woods where resin sea 3 orcompounds of a similar character may formed in considerable amounts. Itmay also contain tanning material, dyes and other dissolved organicmaterial.

The residual liquor is mahogany in color, but -the color varies somewhatin intensity with different woods and is somewhat darker when smallamounts of caustic are used.. In reaction the liquoris alkaline tolitmus but not strongly alkaline'unless caustic has been employed, thedegree of alkalinity obviousl depending upon the amount of caustic used:In consistency the residual liquor may be thinner than black 1i uorscommonly obtained by soda and su phate processes,- and it may contain asmaller proportion of solids in solution because the cellulose is notattacked and dissolved by sodium sul bite to any great extent during thepulp-ma ing operation.

One purpose of the present invention is the recovery of valuableconstituents of the residual liquor, particularly the sulphite radicaland sodium content, sothat these are consequently made available for thetreatmeht offurther quantities of wood. Incidentally,

other valuable and useful products are recovered or made available.

Where a considerable excess of sodium sul of this material in a freestate, and merely by concentrating the residual liquor some of theunconsumed sodium sulphite can be crystallized out upon'the cooling.When the liquor is concentrated directly in this way, exposure to theair during concentration should be avoided as much as possible in orderto prevent conversion of the sulphite into sulphate. This concentrationmay be employed asthe preliminary step in the treatment of the residualliquor, the recovered sodium sulphite being immediately available forreuse while other valuable materials in the residual liquor arerecovered by further treatment.

As a further preliminary step, a portion of the dissolved organic mattermay be separated by treating the residual liquor with suitable acids,rendering it acid in reaction. The precipitated organic matter can thenbe filtered off, leaving a clear liquor containing a decreased contentof dissolved organic matter and being thus more readily susceptible tofurther treatment for the recovery of the sulphite radical and sodiumion remaining therein.

For the further treatment of the residual liquor or for the treatment ofsuch liquor and to displace some of the organic-acid radicals, thusincreasing the yield of sodium,

without preliminary treatment as hereinbefore set forth, the addition ofsulphur dioxide in quantities suflicient to convert sodium com poundsinto sodium sulphite affords an effective method of regenerating sodiumsulphite for reuse as a cooking liquor. Following the treatment withsulphur dioxide, some organic matter present in the solution may beseparated and the liquor is then ready for further use after theaddition of sufficient sodium sulphite to make up the materialconsumedin the cooking operation. A portion of the sodium sulphite may becausticized by the addition of calcium hydroxide if the presence ofcaustic soda in the liquor is desirable.

Where considerable caustic soda has been employed in combination withthe sodium sulphite, as in the treatment of certain woods, sulphurdioxide may be added, (together with sodium bisulphite, the latter beingadded in amount suflicient to make up the loss of soda) to combine withany unusued caustic soda sulphite. If the organic radical released isinsoluble in the neutral or acid liquor, as for example, the resins,gums, etc., a considerable amount of sodium sulphite may be recoveredfrom sodium organic compounds present in the liquor. Thus the residualliquor from the cooking of resinous woods, such as spruce (andespecially pines) contain sodium organic compounds which may beconverted into sodium sulphite by treatment with sulfur dioxide.Following the treatment described, the liquor may be clarified andcausticized to the desired degree by free, and which are more or lesssoluble in the presence of sulphur dioxide. In actual practice,therefore, it may be advantageous to provide for the conversion of thesodium of these organic compounds, which otherwise might concentrate inthe liquor to an objectionable degree, into sodium sulphite or sodiumacid sulphite, and to remove the separated acids or acid compounds. Itmay not be essential, however, that organic compounds of this characterbe removed after every cooking operation since the accumulation may notbe sufficient to prevent satisfactory reuse of the liquor. It issufficient in 'such cases if the organic compounds are decomposed andremoved either wholly or in part after two or more cooking operations.

When the residual liquor contains sufiicient organic matter to interfereWithfurther use thereof in whole or in part as a cooking liquor, theliquor may be treated While neutral or alkaline with gypsum (calciumsulphate) which will react with the sodium sulphite and precipitatecalcium sulphite, leaving sodium sulphate in solution. In this manner,substantially all of the sulphite radical existing as sodium sulphitecan be precipitated from the liquor. Preferably a slight excess ofgypsum is employed to insure complete precipitation. This precipitationmay be carried out either before or after concentration of the residualliquor and the solution containing thesodium sulphate may ,beconcentrated to a-greater or loss degree. So long as the solution isslightwill he precipitated without any appreciable occlusion of organicmatter, and the organic matter will thus remain in solution with sodiumsulphate. The precipitated calcium sulphite may be removed from theliquor by filtration. decantation, sedimentation or otherwise. Thus itmay be' permitted advantageously' to settle so that the liquor may bedrawn off, leaving the calcium sul-, phite for further use ashereinafter described.

The solution containing the sodium sulphate and organic matter may beconcentrated by evaporation or otherwise until the greater portion ofthe sodium sulphate crystallizes out on cooling. Further concentrationof the liquor occurs because of the water taken up as water ofcrystallization by the sodium sulphate. Some psum will crystallize withthe sodium sulp ate but this is unobjectionable. The organic matter willbe left in the solution after crystallization of the sodium sulphatetherefrom and some may be removed by further concentration or byacidification and separation of the resulting precipitate.

The crystallized sodium sulphate may be dissolved, preferably in washwater from the washing of the pulp, and added to the calcium sulphiteprecipitate produced as above described. If an acid such as sulphuricacid or nitre cake (acid sodium sulphate) or an excess of sulphurdioxide is then added, the calcium sulphite will react with the sodiumsulphate, precipitatinggypsum and leaving sodium sulphite in solution.The use of nitre cake as an acidifying agent is desirable inasmuch asthe sodium of the nitre cake is thus added to the liquor, making up anylosses of sodium in the process. The acid solution may be neutralizedwith calcium hydroxide, thus producing a further precipitate of calicumsulphite. The gy sum may be separated from the liquor by ltration,decantation, sedimentation or otherwise and utilized again in thetreatment of further amounts of residual liquor.

The solution of sodium sulphite obtained as above, with properregulation of its concentration, is ready for reuse as a cooking liquor.If a cooking liquor is desired containing caustic in addition to sodiumsulphite, the liquor may be causticized to the desired degree bytreatment with calcium hydroxide.

Instead of concentratin the sodium sulphate solution and crystal izingthe sodium sulphate therefrom, this solution may be concentrated andacidified to precipitate part of the organic matter, and the resultingclear solution may then be treated with the calcium sulphite precipitateto re enerate sodium sulphite in acid solution with precipitation ofgypsum which may be separated from the solution. The excess acid usedfor aciditying the li uor assists in bringing about the reaction 0sodium sulphate and calcium sulphite, or a" further amount of acid maybe added ifnecessary.

It will be noted that the process as described involves the treatment ofthe residual liquor with calcium sulphate'while the liquor is neutral oralkaline with resulting reaction of the calcium sulphate and sodiumsulphite to give a precipitate of calcium sulphite and a solution ofsodium sulphate.

This sodium sulphate solution, after the separation of organic mattertherefrom, is caused to react with the calcium sulphite in the presenceof a suflicient amount of the acid to reproduce the sodium sulphite insolution with precipitation of calcium sulphate. The direction of thereaction thus depends upon 'whether the solution is alkaline or acid.The

sodium bisulphate to give the necessary acidity, they also serve to makeup any losses of calcium and of sodium'in the process.

The concentrated mother liquor after crystallization of the sodiumsulphate therefrom has marked saponaceous properties and can be used asa soap or soap ingredient for industrial purposes, or for the roductionof tanning material and dye stu s. liquor is acidified, organic matteris precipitated in a flocculent condition and the mahogany color of theliquor is destroyed although this color reappears if the liquor issubsequently made alkaline. The liquor obtained from resinous woods suchas pine, when a small amount of caustic alkali is used with the sodiumsulphite during the cooking operation, contains a correspondinglyincreased content of resin soaps and similar materials, and suchliquors, after concentration, will contain correspondingly increasedamounts of saponaceousmaterial which can be recovered therefrom.

If nitre cake alone is used to form sodium sulphate from thesodium-organic compounds, volatile acids such as acetic, formic, etc.,may be set free and removed by heat treatment. Insoluble organiccompounds may be removed by filtration, sedimentation or otherwise, andthe solution of sodium sulphate may be concentrated, e. g., byevaporation and cooling to obtain crystals of-sodium sulphate which arefree from an objectionable amount of organic matter. If the motherliquor from the sodium sulphate crystallization contains considerablesodium sulphate and organic matter, the organic matter may be charredafter evaporation of the liquor and preferably without reduction of thesodium sulphate to sodium sulphide. The sodium sulphate may then bedissolved out of the charredand insoluble materials. sodium sulphatemaybe added to that obtained by crystallization.

If desired, some of the sodium-organic compounds may be decomposed andconverted into sodium carbonate. Any sodium sul- When the This Ill

covered in the process may be causticized with lime and the causticproduced can be added to the sodium sulphite liquor in case a causticliquor is desired, orthe sodium carbonate can be treated with sulphurousacid to form sodium' sulphite. The sodium carbonate may thus be used toneutralize uncombined sulphurous acid in the solution of sodium sulphiteinstead of using calcium carbonate or hydroxide. This procedure insuresthe return of the sodium ion to the solution.

Under certain circumstances, a portion only of the residual liquor needbe converted to produce sodium sulphite when nitre cake is used for theelimination of organic matter from the cycle. The remainder of thesodium organic compounds may be disposed of in any expedient manner.Acetic acid, sodium acetate, etc. may be recovered therefrom and tanningmaterials, dye stuffs, etc. may also be recovered when the residual"liquors contain such constituents.

It may be desirable to eliminate certain steps of the process ashereinbefore set forth and to treat the residual liquor in a relativelysimple manner for the recovery of the more important constituents whilethe organic materials are destroyed. Thus the residual liquor may beevaporated to dryness and the solids may be calcined or burned toproduce sodium carbonate with more or less sodium sulphite, sulphide,etc. These compounds may then be dissolved from the insoluble carbon andtreated with sulphur dioxide or sodium bisulphite or both to eliminatecarbon dioxide and hydrogen sulphide. A product containing sodiumsulphite or a mixture of sodium sulphite and sodium bisulphite may thusbe obtained. Alternatively some of the carbonate may be converted intocaustic soda .and used as such by addition thereof to the sodiumsulphite liquor when a caustic liquor is needed.

When the residual liquor from the cooking of wood with sodiummono-sulphite or a mixture containing a preponderating amount of sodiummonosulphite anda smaller amount of caustic soda is calcined, forexample, in

arotary furnace such as is used in the calcination of the concentratedresidual liquors of the ordinary soda process, a considerabledecomposition of the sodium sulphite or sul phurous acid combinationscontained in the liquors and in the dried product undergoingcalcination, takes place, and a considerable amount of sulphur compoundsescapes with the gaseous products of, combustion by which the rotarycalcining furnace is heated. In such cases, the calcined product willcontain a relatively large amount of sodium carbonate while it may stillcontain varying amounts of sodium sulphite. This method ofproducingsodium carbonate from sodium sulphite is described more fully in ourprior application, Serial No. 513,161, filed Nov. 5, 1921.

, through an absorption tower through which the solution is passed, thisabsorption tower being arranged between the rotary calcining furnacesand the stack, and the necessary draft and circulation of the gasesbeing secured by means of a fan. By using a tower or series of towers inthis way, the sulphur dioxide of the escaping gases can be recovered forreuse in the process. It is an advantage of this method of regeneratingthe sodium sulphite that it permits the use of ordinary calciningfurnaces such as are. available in pulp mills operating according to theordinary soda process, and requires merely the insertion of absorptiontowers and circulating fans between the rotary furnaces and the stack,and the circulation of the leach liquors through the absorption towers.The treatment of the residual liquors can otherwise be carried out inthe same apparatus and with similar manipulation as in the ordinary sodaprocess, although the procedure with theresidual liquors, according tothe present invention, will have. an entirely diferent result owing tothe inherent differences in the residual liquor itself and in thereactions which take place during its treatment. The treatment of theresidual liquors, in the manner described, results in the recovery ofthe greater part of the sodium content as well as of the sulphur dioxidecontent in the form of sodium sulphite in solution available for furtheruse in the cooking operation.

The residual liquors treated will, as above stated, vary in theircomposition and roperties with different kinds of wood. Wit dense hardwoods (for example birch, beech and maple) which have'a considerablygreater weight than poplar wood, the total amount of wood charged into adigester will be a great deal more than the weight of poplar woodcommonly chargeable into the same digester.

The amount of non-fibrous constitutents which such dense hardwoodscontain and which must be removed by the cooking operation, will beradically greater than in the case of a digester of poplar wood. Theamounts of such non-fibrous constitutents in such woods is in fact sogreat that it. is impracticable, with the ordinary soda process, tocarry out a satisfactory cook, owing to the excessive strength andamount of the caustic soda in solution required for the treatment of adigester charge of chips, and the injury which caustic soda of thenecessary increased strength has upon the pulp fibres desired. Suchwoods can nevertheless be satisfactorily cooked with a cooking liquorconsisting essentially'of sodium mono-sulphite or sodium mono-sulphitewith a limited amount of caustic soda, since the amount andconcentration of these reagents in the cooking llquor can the cooking ofsuch woods may have a radi 1 cally increased content both of organicconstituents and of inorganic matter, such as combined .sodium organiccompounds and sulpho-organic compounds. Residual liquors of suchincreased concentration will be somewhat diluted by admixture with washwaters, but dilution to an objectionable degree can be readilyprevented, and the treat- -ment of the more concentrated liquorspresents added advantage because of the de- 2 creased amount of water tobe removed, and

' the radically increased concentration of the constitutents which theliquor contains.

In the foregoing we have described in detail the several operationswhereby we are enabled to recover the chemicals required for thepulp-making operation from the residual liquors resulting from thisoperation, as well as the recovery of valuable by roducts from theliquors. Obviously the details of the procout departing from theinvention, and we claim, therefore, the application of the broadprinciples of the invention as set forth here-' in. Theproceduredescribed eliminates the objectionable features which havecharacterized methods of recovering valuable products from ulp-cookingliquors as heretofore employed and is particularly advantageous inasmuchas it permits the practice of-the pulpmakin operations hereinbeforereferred to at a relatively low cost because of the possibility of're-utilizing the chemicals employed w1 relatively slight additions tomake up for me'vitable losses in conducting these operations. It thuspermits a cyclic operation in which sodium sulphite, with or withoutcaustic soda, is employed as a cooking liquor in the production of pulpfrom various cellulose-containing materials and the regeneration andreuse of the sulphite liquor. This cyclic operation is apart of theinvention herein described and claimed.

In carrying out the cyclic operation, the cooking'of the wood chips canbe carried out, 55 for example, in the manner more full described in ourprior application, Serial No.

481.147, filed June 28, 1921. When the pulp making process. of saidapplication is combined with the regeneration of the cooking liquor, orof ingredients of the cooking liquor,

from the residual liquors, in the manner here'- inbcfore described, thepulp making rocess becomes a regenerative pulp process 0 a particularlyadvantageous character, enabling the pulp mill to operate with thetreatment ess are capable of numerous variations withof the residualliquors and the regeneration of the cooking liquors in a particularlyadvantageous maimer.

Such losses of the ingredients as take place in the process can be. madeup, for-example, in the manner above described. The losses of sodium canbe made up by adding sodiumcarbonate or soda-ash and combinin it'withsulphur dioxide; or by adding sodmm sulphate or salt cake or niter cakein the manner above described. The sulphur dioxide can be supplied tothe necessary extent by simple sulphur burners and by absorption of thegases in alkaline-solutions either or soda-ash or of residual liquors,orof leach liquors resulting from the calcination operations abovedescribed. The amount of sodium sulphite or of sodium sulphite andcaustic soda regenerated from the residual liquors can be supplementedby the necessary additions to give a new cooking liquor suitable forfurther use in the process. 1 I

The regenerative or cyclic process of pulp manufacture, accordinglypresents important advantages in the manufacture of the pulp itself asset forth more fully in our said prior application as well as in thetreatment of the residual liquors in the manner herein described.

This application is a division of our prior application Serial No.534,768, filed February 7, 1922.

We claim:

.1. The process which comprises cooking cellulosic fiber-bearingmaterial in a'solution containing sodium compounds, most of the sodiumcontent thereof eing in the form of a sulfite. of sodium, subjectingresidual liquor derived therefrom to'a treatment including a furnacingstep regulated to burn the combustible content of the residual li uorand to leave a non-gaseous furnace pr uct including inorganic sodiumcompounds derived from the residual liquor, and passing products ofcombustion from such furnacing step in contact with other residualliq-.. nor from such a pulp-making operation for the recovery of solublecompounds there from.

2. The process according to claim 1, in

.which thesolution used in the first named sodium derived from theinorganic mineral content by such furnacing operation, for the recoveryof sulfur-bearing material from such products of combustion.

V 4. The process according toclann 3,1n wh1ch the furnacing and burningtreatment 1s carried out so as to produce a furnace product thatcontains sodium carbonate and a substantial but lesser amount of sodiumsulfid; and in which 'such sodium compounds are dissolved to form analkaline solution, and sodium carbonate thereof isused to recover sulfurdioxide from the products of combustion from such burning operation.

5. A process which comprises cooking cellulosicrfibre-bearing materialin a cooking liquor that contains most of its sodium in the form of asulfite of sodium; separating the spent cooking liquor from theresulting undissolved fibre-bearing material; evaporating watercontained .in the spent cooking liquor, furnacing soli-ds derived fromsuch liquor and burning combustible matter thereof so as to produce anon-gaseous furnace product that contains most of its sodium in the formof sodium carbonate; recovering the resulting sodium carbonate; andpassing the products of combustion from such burning operation incontact with liquor that contains the resulting sodium carbonate torecover sulfur-bearing materials therefrom.

6. The process according to claim 5, in which the said non-gaseousfurnace product contains both sodium carbonate and sodium sulfid.

7. The process according to claim 5, in which the said sodium carbonateis dissolved to form a solution and a solution that contains suchrecovered soda is used to recover sulfur dioxide from such products ofcombustion.

8. The process according to claim 5, in which sulfur dioxide isrecovered from such products of combustion by means of liquor thatcontains carbonate of sodium and such recovered sulfur dioxide isemployed as a sulfite of sodium in a subsequent cooking treatment ofcellulosic-fibre-bearing material.

9. The process for producing pulp, which comprises cooking wood withcooking liquor that contains sodium in the form of a sulfite of sodium;removing residual liquor from undissolved fibre-bearing material;supplymg to other wood and cooking such wood with cooking liquor thatincludes such residual liquor; removing a second residual liquor fromundissolved fibre-bearing material; evaporating water contained in suchsecond res dual liquor; burning combustible matter derived from suchsecond residual liquor so as toproduce gaseous products of combustionwhich carry gaseous sulfur-bearing compounds and so as to recover anon-gaseous furnace product that contains most of its sodium in the formof sodium carbonate; preparing a carbonate; subjecting such solution toa treatment including a sulfiting step so as to convert sodium carbonatethereof into a sulfite of sodium; and cooking wood with cooking liquorthat contains such regenerated sulfite of sodium.

10. The process according to claim 9, in which the said non-gaseousfurnace product contains both sodium carbonate and sodium sulfid and asulfite of sodium is derived from each of these sodium compounds.

11. In a process for producing pulp from wood, the steps which comprisecooking wood in a cooking liquor supplied with a sulfite of sodium;evaporating water contained in the residual-liquor; burning combustiblematter derived from such residual liquor so as'to produce a non-gaseousfurnace product including sodium carbonate; dissolving such sodiumcarbonateand using the same in solution'so as to recover sulfur dioxidefrom products of combustion of the burning step.

12. The process according to claim 11, in which the said non-gaseousfurnace product contains both sodium carbonate and sodium sulfid, thesetwo sodium compounds are dissolved and theresulting solution is used soas to. recover sulfur-bearing matter from products of combustion of theburning step. 13. A process which comprises digesting cellulosicfibre-bearing material with a cooking liquor that contains a sulfite ofsodium, separating a residual liquor from the fibrebearing materials,passing such a residual liquor containing sulfite of sodium and acarvbonate of sodium into contact with herein after-mentioned furnacegases to recover soluble sulfur compounds therefrom, burning combustiblematter of the residual liquor so as to form sulfur-bearing furnace gasesand a non-gaseous furnace product that contains carbonate of sodium,passing such furnace gases into contact with the solution abovementioned, dissolving sodium carbonate from the furnace roduct, forminga sulfite of sodium there rom, and digesting cellulosic fibre-bearingmaterial with liquor containing such regenerated sulfite of sodium.

14. A process according to the preceding claim, in which the firstmentioned cooking liquor is non-acid to litmus and contains sodiumsulfite and a sulfur-free sodium compound that is alkaline to litmus.

In testimony whereof we aflix our signatures.

LINN BRADLEY. EDWARD P. MeKEEFE.

solution that contains such recovered sodium 7

